How To Use Short Burst Intervals for Fast Gains
Comparing Micro vs Long Intervals
You have a long event coming up in 2022 – that big century or gravel ride. While endurance and aerobic capacity is usually built by long and lower-intensity rides, is that the only way? Can you go short to go long?
Anyone that follows me on Strava might be used to seeing some micro-intervals in my workout reports. In addition to making cool looking reports, research has shown that these workouts are highly effective training stimuli. In this month’s toolbox article, I wanted to dig in a little more to understand exactly why those micro-intervals can be so beneficial to your cycling fitness.
Short Interval Benefits
Interval training consists of brief periods of high intensity separated by short periods of recovery. In a past toolbox article, Stephen discussed the benefits of micro-intervals over longer, steady state intervals. Those “bursty” style of intervals are great for mimicking attacks that are present in road & CX racing. But why do these short, hard intervals provide such a potent training stimulus? To help answer that question, I want to direct us to a research paper published by French physiologist, Veronique Billat. I also want to point out that although the study was completed with runners, the basic concept of this research translates well into cycling.
In the late 90’s, it was well known that intermittent training – such as 30s hard efforts separated by 30s of recovery – was both efficient for improving an athlete’s maximal oxygen uptake (VO2max), as well as being tolerable, even for untrained individuals. However, no study had investigated oxygen utilization during these intervals. In a novel study, Billat and colleagues used a portable metabolic analyzer on a track to investigate oxygen utilization during different styles of intervals. We’ll take a quick look at the study subjects & methods below.
- Eight endurance trained male athletes (34 years old) with a very respectable VO2max of 59 mL/kg/min.
- Run #1: Incremental Test to Exhaustion – analogous to doing a ramp test to determine FTP
- Run #2: Intermittent Run – 30s at an effort equal to 100% VO2max, followed by 30s at an effort equal to 50% VO2max. This was continued until exhaustion was reached.
- Run #3: Continuous Run – athletes were instructed to hold an effort around 90% VO2max until exhaustion was reached.
What did they find out?
When looking at the continuous runs, five of the eight runners reached their VO2max and sustained that effort for just under 5 minutes on average. They also reached an average of 96% of maximal heart rate – that’s a painful effort!
How did that effort compare to the intermittent run? On average, the athletes were able to complete 19 repetitions of the hard intervals, which equates to 9.5 minutes of severe exercise at an intensity equal to VO2max. That’s almost double what they were able to achieve during the continuous run! Further, 7 of the 8 runners achieved their VO2max and maintained it for just under 8 minutes, on average. Interestingly, by the 5th interval, researchers saw no significant difference in oxygen consumption between the “on” and “off” efforts, meaning that the athlete’s were almost continually working near VO2max for the duration of the interval session.
The researchers created a beautiful overlaid figure that makes it easy to view & interpret these results – check out the figure from the study posted below. The figure displays one athlete’s oxygen consumption on the left axis plotted against the duration of the run on the horizontal axis. In the black dots, you can see this athlete’s continuous running session, while the intermittent run is displayed in the white triangles.
Taken from Billat et al., 2000.
I want to point out a couple of things from this figure. First, this graph makes it easy to see how much more training can be accomplished when utilizing micro-intervals. Although both efforts were completed to exhaustion, the intermittent effort could be sustained far longer. What I find even more interesting is that athletes were able to maintain such a high oxygen consumption throughout the effort. So, not only can these intermittent intervals be sustained for longer, but they also allow athletes to spend a large amount of time near VO2max.
I’ll provide an example of how I have added in some Billat-style efforts into my winter training… After an extended warm-up, my goal with these HIIT sessions was to complete repetitions of 30 sec at 370 W (approximately my 4-minute power) followed by 30 sec recoveries at ~120 W. I don’t always aim for an exact power target, but also guide the effort by my perceived effort (9/10 on the ‘on’ intervals) and heart rate, aiming to stay around 85-90% of max HR. The result is something that looks something like this:
An Xert power file of Billat-style workout. My Power data is shown along the bottom of the page (red/blue), the purple is Xert’s model of “Maximal Power Available” or MPA. The red line is my Heart Rate. In this activity, I was able to sustain ~89% of my maximum heart rate for 30 min.
The key finding of this study was that intermittent running, alternating between 100% VO2max and 50% VO2max, allowed runners to maintain VO2max significantly longer than a continuous interval around 90% VO2max. The authors mentioned that the benefit of high intensity training on aerobic capacity (VO2max) is dependent on the time spent training at VO2max. Thus, they concluded that intermittent training was superior to continuous intervals, since intermittent workout allowed for a greater amount of time spent at VO2max.
Because the study compared only two high-intensity sessions, the authors were unable to conclude on the chronic results of intermittent intervals. However, their speculations were later confirmed by Dr. Rønnestad’s work, demonstrating that 3 weeks of training with short intervals resulted in superior performance improvements when compared to long-intervals.
That’s all for this time – Stay safe and ride fast. I’ll see you next month.
A long interval for Wout
Billat VL, Slawinski J, Bocquet V, Demarle A, Lafitte L, Chassaing P, Koralsztein JP. Intermittent runs at the velocity associated with maximal oxygen uptake enables subjects to remain at maximal oxygen uptake for a longer time than intense but submaximal runs. Eur J Appl Physiol. 2000 Feb;81(3):188-96.
Rønnestad, BR et al. Superior performance improvements in elite cyclists following short-interval vs effort-matched long-interval training. Scand J Med Sci Sports. 30:849-857, 2020.